To meet recent-year trends such as higher buildings and larger-scale buildings, there has been an increasing demand for concrete (a cementitious material) that exhibits a high level of compressive strength and bending strength. One of means for imparting such characteristics is a technique of adding any of metal fibers, resin fibers, inorganic fibers, and the like (hereinafter generally referred to as “concrete-reinforcing fibers”) to concrete (see PTL 1).
Concrete-reinforcing fibers each have a diameter of several tenths of millimeters and a length of several tens of millimeters (see PTL 2 and 3). Concrete-reinforcing fibers are stored in a drum or the like. To feed such concrete-reinforcing fibers into a concrete-mixing machine, the concrete-reinforcing fibers are taken out of the drum and are sieved before being fed into the mixing machine.
In such a process, for example, even if piles of concrete-reinforcing fibers are fed in units of about 2 kg, about 30% of the concrete-reinforcing fibers tangle together into blocks of concrete-reinforcing fibers, which are called fiber balls. Fiber balls thus generated may trigger deterioration in the quality of concrete. In the worst scenario, a whole batch of concrete may need to be disposed of, the number of times of cleaning of the mixing machine after such disposal may increase, or the mixing machine may be damaged.
Hence, in the known art, concrete-reinforcing fibers are fed from the drum into the mixing machine through a sieve.